As far as making the playoffs, I believe there is only one question to ask! Does your team have the TALENT to win a championship? If yes, then definitely go for that playoff spot (ie., the Nets--not playing that good, but have enough players with talent to win if everything came together)
If no, you go for that draft pick!
I believe it's pretty black and white.
I think there are times when a team may not have the talent to win it all, but making the playoffs is definitely a good thing.
Teams like the Kings, Wizards, Cavs -- they've spent years in the lottery and have collected some significant talent.
Now is the time for those teams to finally get some experience and start to figure out how to win together. Those teams are all probably one or two pieces away, but they've got some good core pieces.
If you have a young team with a star prospect or two, I think it's good to make the playoffs as long as you don't compromise salary flexibility in the future in order to do so. Because though your team might be a 7th or 8th seed, one free agent addition like Boozer or David West could be enough to vault into the upper echelon, as was the case for the Bulls and Pacers.